Mozilla Patches Critical Firefox Security Flaws

Mozilla patched Firefox 4 to close a major security vulnerability that exposed the browser to attack on all Windows systems. Mozilla also fixed issues in earlier versions of its popular Web browser.

Firefox developers addressed a total of 53 bugs in Firefox 4 and earlier, of which 12 were rated “critical” and nine were categorized as “major,” Mozilla said April 28. The majority of the critical issues are related to systems crashing and freezing while others dealt with issues in which large Adobe PDF documents could not be properly loaded in the browser.

Mozilla developers fixed memory corruption bugs (MFSA2011-12) in the browser engine that could be corrupted under “certain circumstances,” according to Mozilla. “With enough effort, at least some of these could be exploited to run arbitrary code,” the advisory said.

A programming error in Firefox 4 potentially exposed the latest version of the browser to “two crashes” that could be remotely exploited to run malicious code, Mozilla said. The WebGLES graphics libraries that support open-source WebGL were compiled without ASLR, or Address Space Layout Randomization, protection before they were used in the Windows versions of Firefox, according to Mozilla advisory MSFA 2011-17.

This is a critical programming oversight, as ASLR is designed to make it difficult for attackers to locate addressable memory space to execute exploits. Windows Vista and Windows 7 rely on ASLR for its security, and attackers would be able to compromise the operating system by bypassing Firefox’s WebGLES libraries.

"An attacker who found an exploitable memory corruption flaw could then use these libraries to bypass ASLR on Windows Vista and Windows 7, making the flaw as exploitable on those platforms as it would be on Windows XP or other platforms," Mozilla said in its advisory.

WebGL, an open-source extension to JavaScript, lets developers render interactive 3D graphics content. It is supported in Firefox, Google’s Chrome Web browser, and is expected to be included in the next versions of Opera and Safari.

Two bugs related to WebGLES were fixed in Firefox 4.0.1. The bugs are present only in Firefox 4, as WebGL wasn’t used in previous versions of the browser, according to Mozilla.

Mozilla also upgraded Firefox 3.6 and 3.5, but warned that 3.5.19 was the last planned security and stability release for Firefox 3.5. Users were encouraged to upgrade to Firefox 4. The update for Firefox 3.6 addressed the same memory corruption bug in Firefox 4.

A “dangling pointer” bug (MFSA2011-13) was fixed in Firefox 3.6. A dangling pointer is a programming error in which a memory reference remains active even when the object it pointed to is no longer in use. Another 3.6-specific vulnerability dealt with privilege escalation in the Java Embedding Plug-in (MFSA2011-15).

"Apple users who imagine themselves invulnerable simply by virtue of their choice of operating system, please take note," warned Paul Ducklin, head of technology for the Asia-Pacific region for Sophos.

Firefox 4 was launched March 22. Mozilla posted the first build of Firefox 5 on May 2, and expects to have a first beta release on or around May 17. Mozilla is moving to a six-week product cycle for its Web browsers.